Self-bulking conjugate filaments



United States Patent 3,505,164 SELF-BULKING CONJUGATE FILAMENTS George C. Oppenlander, Embreeville, Pa., assignor to Hercules Incorporated, Wilmington, Del., a corporation of Delaware No Drawing. Filed June 23, 1967, Ser. No. 648,207 Int. Cl. D02g 1/00 US. Cl. 161-173 3 Claims ABSTRACT OF THE DISCLOSURE Conjugate filaments exhibiting a high degree of spontaneous crimp can be prepared from polypropylene and a crystalline copolymer of propylene and up to about 25% of a second a-olefin. Two component filaments are preferred, although more can be used if desired. Components are in side-by-side relationship.

This invention relates to synthetic fibers which exhibit a high degree of bulk or crimp. In particular, it relates to polypropylene filaments of novel configuration which crimp or bulk spontaneously.

In recent years, synthetic fibers have come to assume an increasingly larger position in the textile market. Where wool and cotton were at one time virtually unchallenged as the materials employed by the textile industry, they are now being replaced in many applications by nylon, polyester, and acrylic fibers, and more recently by the olefin fibers, particularly polypropylene. The synthetic fibers possess properties such as ease of care, durability, mechanical strength, and warmth, with light weight, to name a few, which are not found in the older,

. natural textile materials.

However, wool fabrics have advantages of their own which to date have been extremely difficult and expensive, if at all possible, to reproduce in the synthetics. Principally, the woolen yarns or fibers possess a high degree of natural crimp. This results in their exhibiting a high bulk and excellent covering properties as well as good elastic properties such as stretchability, compressional resilience and liveliness. In addition, wool has a very pleasing surface feel or handle which consumers have come to prefer.

Many attempts have been made to prepare synthetic fibers or yarns which, when converted into a fabric, would result in a product exhibiting the desirable properties of wool in addition to the desirable properties of the synthetic. Many of these attempts take the form of methods to impart a crimp to the synthetic yarn. The most successful such attempts have been those which impart a spiral or helical crimp.

It has been proposed to impart a helical crimp by spinning the synthetic polymer in the form of a conjugate filament having two or more different, though usually, related polymers joined in side-by-side or sheath and core relationship. When the filament is drawn in the customary manner known to the synthetic fibers art, and thereafter relaxed, the different polymer segments exhibit different relaxation or shrinkage potentials. This differential shrinkage results in helical coiling of the individual filaments. When such filaments are collected into a yarn, the resultant yarn assumes a high bulk due to the difficulty experienced by the helically-coiled filaments in remaining in close proximity to one another.

In British Patent 979,003, it is proposed to prepare a self-bulking filament of polypropylene by spinning a conjugate filament comprised of two different polypropylene components which differ in their intrinsic viscosities by a specified amount. The differential shrinkage of the two polypropylene components causes the previously referred to helical coiling when the yarn is relaxed after stretchmg.

It has now been found that conjugate filaments exhibiting a high degree of spontaneous crimp can be prepared from polypropylene and a crystalline copolymer of propylene and up to about 25% of ethylene or of an a-olefin having up to 6 carbon atoms. These filaments, upon drawing followed by relaxation, can assume a helical crimp of about 5 to crimps per inch.

The conjugate filaments of the instant invention, un like those of the prior art, as exemplified by British Patent 979,003, above, do not depend upon differences in intrinsic viscosity, molecular weight or molecular weight distribution for the formation of crimp. This is advantageous since it is not always a simple matter to tailor polymers to precisely the desired differential in such properties. It is relatively easy, however, to provide copolymers which are distinct from homopolymers.

Another advantage of the conjugate filaments of this invention over those of the prior art containing a homopolymer as each component of the filament is in the mechanism by which the crimping by differential shrinkage comes about. In homopolymer conjugates, it has been found that, in order to produce the optimum in crimp level, the filaments must be drawn under conditions such that a relatively high concentration of so-called mircovoids are formed in oneand only oneeomponent of the conjugate entity. These micro-voids are actual void spaces in the polymer structure believed to be caused by the pulling apart of polymer crystals during drawing. Such voids are not visible to the naked eye but collectively, they give the filament a chalky ap earance. When the yarn is heated to effect shrinkage, shrinkage takes place by (1) disorientation of the polymer molecules and (2) closure of these voids. In homopolymer conjugates the greater effect has been found to come from void closure, resulting in greater shrinkage by the voided component. The process conditions, however, are rather critical, requiring specific temperature levels to be maintained at each stage thereof from spinning thru relaxation in order to assure that a high level of voiding is made to occur in only one component and that the major shrinkage effect comes from void closure.

Voiding of one of the components, however, does not enter into the formation of helical crimp by differential shrinkage of components of the filaments of this invention. In fact, drawing is carried out under conditions under which substantially no voiding of either component takes place. Thus the potential problems and pitfalls of the voiding phenomenon are avoided.

The useful polymers and copolymers of propylene in this invention are those which contain a substantial degree of crystallinity. Since crystallinity is not conveniently measured, however, it is more convenient to define the same in terms of the density of the polymer. Thus, it is known that a totally amorphous copolymer of ethylene and propylene or a totally amorphous (atactic) homopolymer of propylene has a density of 0.85. A totally crystalline homopolymer of propylene has a density of Particularly useful copolymers are those of propylene and a second a-olefin which are crystalline and which contain a maximum of about 25% of the second olefin. These can be of the block or random type. In the following description the copolymerization process will be described with ethylene as the second monomer. The processes, however, are equally applicable to preparation of copolymers of propylene with other a-olefins having up to 6 carbon atoms.

Block copolymers are those which are predominantly composed of isotactic polypropylene chains but which contain one or more blocks of either ethylene homopolymer or ethylene-propylene copolymer in the molecule. These copolymers normally contain about 3 to 25% ethylene. Such products are prepared by the sequential polymerization of (l) propylene and (2) either a mixture of propylene and ethylene or ethylene alone, or vice versa. The most convenient method for making such compositions is to homopolymerize propylene in the presence of a stereospecific catalyst in a liquid diluent to form a homopolymer and then introduce ethylene while there remains some unpolymerized propylene in the reaction vessel. At this point the polymerization continues as a copolymerization. In theory, the product of such a process is intended to be composed of macromolecules in which one or more segments of the homopolymer of the propylene (PP) alternate with one or more segments of a random copolymer of the propylene with ethylene (EP) to form products having the theoretical structure:

( (PPEP),,PP

where n represents an integer of one or more depending on the number of polymerization sequences. If polymerization of the ethylene monomer is continued after the exhaustion of the propylene the theoretical repeating unit will have the structure (P'P-EPEE) where EE represents a homopolymer of ethylene. However, there is evidence that the socalled block copolymer is actually an intimate mixture of a homopolymer of the propylene and a coplymer of the two monomers and, optimally, homopolymer of the ethylene, the mixture being homogeneous in the sense that there exists a uniform dispersion of the component polymers throughout the product. Hence, in using the term block copolymer it is not intended to restrict the meaning to polymeric compositions of true block copolymer structure, but rather it is intended to include the compositions commonly referred to as block copolymers even though such may not be precisely the case. Such copolymers preferably have intrinsic viscosity of about 2 to 4. Block copolymers of these and other types and their formation are taught in US. 3,301,921, Australian Patent 253,751, British 889,230, British 915,662 and French 1,290,523 inter alia.

Random copolymers, sometimes referred to as statistical copolymers are those wherein the ethylene is distributed throughout the molecule not according to a predetermined plan, but randomly depending upon the relative concentrations of the two monomers in the reaction mass. This type polymer is prepared by continuously feeding both ethylene and propylene at a predetermined ratio. The resulting polymer is crystalline as de fined above (i.e., density of at least 0.88) when the ethylene content is less than about 10%, preferably about 2 to 5%.

The properties of the polymers employed in the various components of the conjugate filaments are not critical for use in this invention in any way that they are not critical for typical synthetic filament applications. Thus the density limits specified above are those normally contemplated for any filament application. The same is true of the intrinsic viscosity range of about 1.5 to 4.

As is also usually the case with polypropylene in more traditional synthetic filament applications, heat stabilizers, light stabilizers and antioxidants are also included in the formulations. Any of the stabilizer-antioxidant systems normally employed for this purpose can be used. These are well known to the art and need not be discussed here. Other additives as dyeing adjuvants, pigments, and fillers can also be included.

The ratio of the components in the conjugate filaments of this invention can vary from about 1 to 4 to 4 to 1. Usually, however, the filaments will be comprised of about equal portions of each component.

The different components of the filaments can be arranged in either side-by-side or sheath and core configuration. Normally, the side-by-side arrangement is satisfactory and preferred. The sheath and core arrangement is normally employed in cases where there is a significant difference in properties between the polymers in the two components, e.g., where one is less durable, or less stable, or less chemically inert than the other. The sheath and core arrangement allows the inner component to be protected by the outer components. In the instant case, very little difference in properties other than shrinkage potential exists between components. Thus, there is usually no need for the protection afforded by the sheath and core. However, if other considerations make it desirable, the sheath and core arrangement can be employed.

Generally speaking the preparation of the filaments is accomplished according to standard methods except for the simultaneous spinning of a multiplicity of polymer streams. That is to say, the polymer is extruded under pressure in the form of a melt through an orifice and subjected to a substantially non-orienting melt draw down whereby the thickness of the filament is reduced. Thereafter the shaped filament is subjected to a cold, orienting draw. The crimp is then developed in the drawn yarn by heating the same While in a substantially tension free state.

Spinning equipment suitable for preparing filaments of either of these configurations is well known in the art and forms no part of this invention. For disclosures of equipment for forming these filaments, reference can be had to US. 3,192,562, 3,181,201, 3,176,346, 3,176,345, 3,176,343, 3,176,342, 3,161,914 and many others.

The basic design feature of these spinnerets is the provision of polymer in more than one stream with the streams converging and contacting each other at a point at or immediately before the extrusion orifice. Specific spinneret design determines whether the resulting filament possesses the side-by-side or sheathcore configuration. Contact between the streams is always made while the polymer is molten so that the several components can fuse into a single, well adhered composite structure upon cooling. Spinning can be accomplished at a temperature between 190 and 325 C. preferably about 250 to 300 C. p

In most cases, spinning is etfected through a spinneret having a plurality of conjugate orifices in its face. The resulting plurality of conjugate filaments is usually collected together into a yarn which is then subjected to the remainder of the treatment steps as an entity. When the yarn has undergone the drawing and relaxation steps, it assumes substantially greater bulk due to the helical coil or crimp imparted to the individual filaments.

The orienting draw is conducted at a temperature below the melting point of the polypropylene in order to develop the optimum properties of the filaments but above the temperature at which either of the components forms voids. Preferably, the drawing temperature will be between about and C. in order to develop the optimum in tensile properties and also to develop the necessary differential shrinkage potential. A draw of at least about is required to produce sufiicient shrinkage to result in useful crimped filaments or yarn. 1

Drawing is effected according to techniques well known in the art. A preferred method is drawing in the narrow .causes the same to shrink, bringing the differential shrinkage eifect into play. Heat treatment is preferably effected in a batch operation, as with boiling water or an oven, at a point above the point where the copolymer component shrinks, but below that at which substantial shrinkage of the homopolymer component takes place. Normally this will be between about 90 and 150 C. The specific temperature selected is also dependent upon the ethylene content of the copolymer component with higher temperatures being preferred at the lower levels of ethylene content. The heat treatment is carried out for about 0.2 to minutes. It is also possible to carry out the heat treatment continuously by bringing the yarn, moving at a high speed, e.g., 100 to 1000 meters per minute, into contact with a hot plate or through a heated zone. In such a case, due to the high rate of yarn travel, the contact time of the yarn with the heat treatment is less than during a batch operation and accordingly higher temperatures are employed. In continuous operation, treatment times on the order of 0.01 sec. to about 1 minute are employed. The heat source or the zone can be at a temperature as high as 300 C., since the contact time of the yarn with the heat source will be so short that the yarn will not reach the temperature of its environment. The higher temperature will permit absorption of sufficient heat to effect shrinkage during the short contact period. Using this mode of operation, however, provision must be made to allow shrinkage of the yarn without appreciable tension development. If tension develops, the yarn will either break or heat set so that no bulk will develop.

The filaments prepared according to this invention can have a crimp frequency of about 5 to 100 crimps per inch (c.p.i.). The crimp frequency is related inter alia, to nature of the components, the draw ratio, draw temperature, and the relation temperature and tension. Normally a crimp frequency of about 5 to 40 c.p.i. is satisfactory.

This invention is illustrated by the following examples, in which parts and percentages are by weight unless indicated otherwise.

EXAMPLE 1 Using a spinneret of the type shown in British Patent 979,083, having 35 orifices of 0.016 inch diameter, a conjugate filament yarn was spun from propylene homopolymer and a random copolymer of ethylene and propylene containing about 2.4% ethylene the components being disposed in side-by-side relationship. Both compoponents contained, as a heat stabilizing additive 0.15% by weight of the reaction product of 1 mole of acetone with 2 moles of nonyl phenol. The homopolymer had intrinsic viscosity of 2.2 and density of 0.90, and the copolymer had intrinsic viscosity of 2.0 and density of 0.90. Spinning was effected at 250 C. at a linear rate of 665 meters per minute to form a spun yarn having a denier of 352.

The spun yarn was drawn about 3.5 X using differentially driven feed and draw rolls operated at a linear speed of about 39 and 137 meters per minute respectively. The feed roll temperature was 93 C. and that of the draw roll was 100 C.

Visual inspection of the yarn indicated that no void formation had taken place as a result of the drawing. The 3.5x drawn yarn was heated under substantially no tension by placing a skein of the same on a metal grating in an oven at C. for two minutes. A helical crimp on the order of about 30 c.p.i. resulted.

EXAMPLE 2 Example 1 was repeated, using the same homopolymer in combination with an end block copolymer containing about 25% ethylene. The resulting yarn was heat treated in boiling water for five minutes to form a helical crimp of about 40 c.p.i.

EXAMPLE 3 Example 1 was repeated using the same homopolymer and a 3-block copolymer containing 3% ethylene. Upon heat treatment in boiling water a helical crimp of about 25 c.p.i. developed.

Example 1 was repeated using the same homopolymer and a random copolymer of propylene and about 3.2% butene-l. The resulting yarn was heat treated in an oven at 125 C. for 5 minutes and formed a helical crimp of about 20 c.p.i.

While the invention has been described above in terms of filaments comprised of one homopolymer component and one copolymer component, it should be recognized that it is not thus limited. The invention also contemplates filaments having more than two components, such as e.g., a homopolymer and two copolymer components. In most cases, however, two components provide sufiicient variation between components to cause the desired amount of crimping. Also, as the number of components increases, the degree of sophistication of the extruding equipment, and thus the difliculty and expense of fabricating the same, likewise increase. In only a few cases will it be necessary or desirable to prepare filaments having more than two, or at most, three components.

It is also within the scope of the invention to prepare conjugate filaments with polypropylene in one component and a mixture of copolymers in the other components, e.g.., a mixture of ethylene-propylene and butenepropylene copolymers.

What I claim and desire to protect by Letters Patent is:

1. A conjugate filament comprised of at least two components disposed in side-by-side relationship, one component being polypropylene homopolymer having a density of at least about 0.88 and another component being a copolymer of propylene and up to about 25 of a second a-olefin having 2 to 6 carbon atoms, and having a density of at least about 0.88, the ratio of homopolymer to copolymer being Within the range from about 1:4 to 4: 1, said filament having been cold drawn at least about and having a crimp of about 5 to 100 helical crimps per inch.

2. The conjugate filament of claim 1 having two components in which the copolymer component is a random copolymer containing about 2 to 5% ethylene.

3. The conjugate filament of claim 1 having two components of which the copolymer component is a block copolymer containing about 3 to 25 ethylene.

References Cited UNITED STATES PATENTS 2,200,429 5/1940 Perrin et al. 2,912,424 11/1959 Cash 26088.2 3,038,236 6/1962 Breen 161l77 3,268,624 8/1966 Iezi et al 260-88.2 3,315,021 4/1967 LuZZato 264-168 FOREIGN PATENTS 985,717 3/1965 Great Britain.

ROBERT F. BURNETT, Primary Examiner LINDA M. CARLIN, Assistant Examiner U.S. Cl. X.R. 161-177 

